The endothelium forms the luminal surface of the vascular system, and is an integral component in such physiologic functions as wound healing, hemostasis, selective transfer of substances to and from the circulation, and synthesis of numerous metabolically active compounds. Correspondingly, endothelial involvement is prominent in pathologic conditions including atherosclerosis, diabetes, thrombosis, hemorrhagic disorders, tumor metastasis, hypersensitivity, and inflammation (Levine et al Biochemical Interactions at the Endothelium, Elsevier, Amsterdam (1983) pp. 313-342). The need for a greater understanding of endothelial function has prompted methodological improvements for culturing this cell in vitro. Bovine endothelial cells have been studied widely due to the ease with which they can be serially subcultivated (Levine et al, supra; Rosen et al J. Cell Physiol. 107. 123 (1981); Mueller et al, Science 207, 889 (1980)). Human endothelial cells, however, have more fastidious growth requirements and, despite a suggestion that fibroblast growth factor and thrombin stimulate their growth, (Gospodarowicz et al, J. Cell Biol. 77, 774 (1978)), little progress has been made in the long-term serial subcultivation of these cells (Maciag et al , J. Cell Biol. 91, 420 (1981); Glassberg et al, In Vitro 18, 859 (1982); (Johnson, J. Clin. Invest 64, 841 (1980); Gimbrone, Jr., et al, J. Cell Biol 60, 673 (1974); Jaffe et al, J. Clin. Invest. 52, 2745 (1973); Haudenschild et al, J. Ultrastruct. Res. 50, 22 (1975); Gordon et al, J. Cell Biol. 91, 205A (1981)).
A significant advance in this field was the use of endothelial cell growth factor (ECGF) and fibronectin to enhance the replicative capacity of human umbilical vein endothelial (HUVE) cells (Maciag et al., supra). These factors allowed HUVE cells to be subcultivated; however, multiplication was slow (2-3 day doubling time) and these cells exhibited a short lifespan (27-34 population doublings (PDs)). Human endothelial cells isolated from adult iliac artery and grown under the same conditions exhibited an even shorter lifespan (15-18 PDs) (Glassberg et al, supra). In no case have cloned strains of human endothelial cells been reported.